this is what i wear in the summer...it isn't too bad as far as heat goes. i wouldn't want to go for a jog in it, but even at slow speeds, it is not unbearable and at highway speeds it is actually pretty comfortable even at 95* and high humidity.
i consider it (at least close to) ATGATT, but some might not.
on my feet, i wear smartwool socks (don't let the "wool" part fool you...smartwool socks are great in hot weather) and fox comp 5 shorties (half height MX boot).
between my feet and waist, i sometimes wear a base layer of underarmor heat gear (meaning "designed to keep you cool" gear) tights. sometimes, no base layer. no base layer is a bit cooler, though the UA does a great job of wicking and does not add too much heat. however, i like the base layer as it prevents the straps on my knee/shin guards from irritating my skin.
then, i wear alpinestars reflex knee/shin guards and alpinestars bionic freeride shorts (with CE rated armor...similar to what the OP described). over that i wear duluth trading company firehose cargo pants. they aren't leather, but seem like the would provide decent abrasion resistance (i have not had to test them, though), and they breath better than even regular jeans...and certainly better than leather. (also, the bionic free ride shorts have hard armor over the hip/quad area where much road rash seems to happen...and the tailbone)
(duluth firehose clothing is made out of the same material they wrap firehoses in to keep them from getting destroyed when being dragged around on pavement and run over by cars. it seems pretty similar to carhartt stuff, but is more supple/comfortable and breathes better, imho. it's not leather, but definitely way tougher than regular jeans.)
on my top half, i wear a long sleeve underarmour heat gear shirt with an alpinestars bionic II "jacket" (really a zip up compression suit with CE rated armor). if it is really hot out and i am not going to be riding at high speeds for long, i just wear a loose fitting synthetic t-shirt over the bionic II "jacket".
if it isn't terribly hot, i wear a firehose jacket over the bionic II for extra abrasion resistance.
the bionic II with just a shirt over it does leave a few small areas open to possible road rash, but the shoulders, elbow, forearms, back, and chest (i.e., most likely road contact points) all have good, hard armor on them that is tightly held in place. further, this set up is very cool (temp wise, not fashion wise
). even sitting still at red lights, i don't get *too* hot. and moving at any speed above 15mph or so is no problem at all.
what made the biggest difference for me, though, i think was starting to wear my MX helmet and goggles instead of a full-face street helmet on the street in the summer. yeah, my full face helmet (which i what i wear on the road in cooler weather) does provide better protection, but the MX helmet with googles is still pretty good protection and *waaaaaaaaayyyyy* cooler for me. and your head is key in regulating your body temp, so a cooler helmet will make a big difference.
ymmv, of course. but, for me, this set up is way cooler than leather. i like the compression suit over an armored textile jacket because i think it will keep the armor in place better. also, all this gear doubles as decent off road gear, so i have one set of gear that works pretty well both on and off road. er, well, i have crash tested it (more than once) off-road, and it definitely has done the job there. fortunately, i have not crash tested it on the road (and hope i don't), so i can't really say how it works in a road crash. i think it would give pretty good protection, though, and i know it is not nearly as hot as leather.
(and, no, i don't work for alpinestars...it's just that, when i was looking for this stuff, they were the only ones i could find that that had shorts with hard armor instead of just foam and the only compression suit i could find with CE-rated armor.)
(also note that i ride a DRZ and it does not generate much heat on my legs like some of you guys are describing with other bikes...though i think the firehose pants might actually deal with that OK, but i dunno.)